Desulfurizing agent for molten pig iron

ABSTRACT

A DESULFURIZING AGENT FOR MOLTEN PIG IRON IN THE FORM OF MOLDINGS OF A HOMOGENOUS COMPOSITION CONSISTING OF 60 TO 85% BY WEIGHT OF SODA ASH (ANHYDROUS SODIUM CARBONATE), 3 TO 25% BY WEIGHT OF PORTLAND CEMENT, AND ALSO 0 TO 10% BY WEIGHT OF WATER GLASS, 0 TO 5% BY WEIGHT OF BORAX, 0 TO 5% BY WEIGHT OF SODIUM CHLORIDE, 0 TO 10% BY WEIGHT OF A CALCIUM-CONTAINING SUBSTANCE, 0 TO 5% BY WEIGHT OF A CARBONACEOUS SUBSTANCE, AND 0 TO 10% BY WEIGHT OF IRON POWDER, CONTAINING ALSO 7 TO 15%   BY WEIGHT OF WATER, WITH AN APPARENT SPECIFIC GRAVITY OF 1.3 TO 2.5, SAID MOLDINGS HAVING ONE OR MORE THROUGH HOLES OR GROOVES EACH.

g- 1972 MASARU TAKASHIMA ETAL 3,681,051

DIJISULI-URIZING AGENT FOR MOLTENPIG IRON Filed Dec. 4, 1969 3 Sheets-Sheet l INVENTORS. MASARU TAKASHIMA MASAO SAITO 3y SHIGERU MATSUYAMA KAZUFUSA UEKI Una m (@014 6 0mm 57mm.

ATTORNEYS.

Aug. 1, 1972 MASARU TAKASHIMA ETAL SULFURIZING AGENT FOR MOLTEN PIG IRON 5 Sheets-Sheet 2 Filed Dec. 4, 1969 1972 MASARU TAKASHIMA ETAL 3,681,051

DESULFURIZING AGENT FOR MOLTEN PIG IRON :5 Sheets-Sheet 5 Filed Dec. 4, 1969 .W. A 0 Y A m H GR E m m O I xmnn mm TA A MW S S U U6 RO F AA U 6 fi w HA MMSKQW Y W B h M MN UnitedStates' Patent 01 ace 3,681,051 Patented Aug. 1, 1972 3,681,051 DESULFURIZING AGENT FOR MOLTEN PIG IRON Int. Cl. czlc 7/02 U-S. CL 75-58 1 Claim ABSTRACT OF THE DISCLOSURE A desulfurizing agent for molten pig iron in the form of moldings of a homogeneous composition consisting of 60 to 85% by weight of soda ash (anhydrous sodium carbonate), 3 to 25% by weight of portland cement, and also to 10% by weight of water glass, 0 to 5% by weight of borax, 0 to 5% by weight of sodium chloride, 0 to by weight of a calcium-containing substance, 0 to 5% by weight of a carbonaceous substance, and 0 to 10% by weight of iron powder, containing also 7 to by weight of water, with an apparent specific gravity of 1.3 to 2.5, said moldings having one or more through holes or grooves each.

The present invention relates to an agent for desulfurizing molten pig iron.

For the removal of sulfur from molten pig iron outside the furnace, it has been customary to introduce a desulfurizing agent consisting of an alkali or alkaline earth metal compound into the ladle or mixer or receiver, and to allow the charge to stand or to agitate the molten metal by means of an external force so as to effect a reaction between the molten metal and the agent for desulfurization. To agitate the molten pig iron with an external force, usually a shaking ladle is used or an inert gas is blown in. These and similar other methods in use are invariably effective but are not desirable for the treatment of a large quantity of molten pig iron because they call for large power and involve much complicacy in operation. While a conventional method of agitating the melt by pouring it into another vessel is convenient for the mass treatment, the difierence of specific gravity between the molten metal and the desulfurizing agent leads to floating of the latter over the former and therefore to the elimination of sulfur from the metal surface only. The result is a low rate of desulfurization, usually in the range below 40%. Other disadvantages include, in the case of a desulfurizing agent in powdery form, the possibility of a fairly large part of the desulfurizing agent being lost by scattering.

The present invention aims at improvements in a desulfurizing agent of particular formulation and shapes adapted to increase the usual desulfurizing rate without resorting to any of the complicate procedures and with no possibility of loss by scattering of the agent itself as above described, and also of an agent which is easy to operate for the desulfurization of molten pig iron outside the furnace.

The desulfurizing agent to be molded into blocks of many different shapes according to the present invention is composed essentially of soda ash (anhydrous sodium carbonate) and portland cement, containing, where necessary, much smaller proportions of water glass, borax, sodium chloride, a calcium-containing substance such as calcium oxide, calcium carbonate, calcium hydroxide, calcium fluoride, or calcium chloride, a carbonaceous substance such as coke dust, graphite powder, or charcoal powder, and iron powder.

The composition and shape of the desulfurizing agent for molten pig iron according to the present invention are such that the agent consists of 60 to by weight, preferably 70 to 83% by weight, of soda ash (anhydrous sodium carbonate) and '3 to 25 by weight of portland cement, mixed, according to the necessity, with 0 to 10% by weight of water glass, 0 to 5% by weight of borax, 0 to 5% by weight of sodium chloride, 0 to 10% by Weight of calcium-containing substance, 0 to 5% by weight of carbonaceous substance, 0 to 10% by weight of iron powder, and contains 7 to 15% by weight of water, and the homogeneous composition thus obtained which has an apparent specific gravity of 1.3 to 2.5 is molded to a block or the like having one or more holes or grooves formed therethrough.

Moldings of the desulfurizing agent and the procedures for the removal of sulfur with such moldings in accordance with the present invention will be more fully described hereunder with reference to the accompanying drawings, in which:

FIGS. 1 to 7 are perspective views of a desulfurizing agent molded to different forms in accordance with the present invention;

FIGS. 8 to 10 are perspective views of fragmentary parts of an expanded metal and perforated iron sheets to be used in the process of the invention;

FIG. 11 is a perspective view of an assembly of molded blocks of the desulfurizing agent supported by an iron framed base and covered on top with a punched iron sheet to a unitary construction;

FIG. 12 is a vertical sectional view showing the lower part of a ladle for molten pig iron that contains a unitary assembly as illustrated in FIG. 11;

FIG. 13 is a perspective view of a cubic assembly of molded pieces of a desulfurizing agent bound together as if crated with flat steel bands; and

FIG. 14 is a perspective view of an exemplary molded block of a desulfurizing agent which is formed with a multiplicity of through holes.

FIGS. 1 to 7 illustrate some examples of shapes in which the moldings may take. The moldings may be either blocks such as shown in FIGS. 1 and 2 which are substantially cubic with fiat horizontal surfaces 1 on top and bottom for the facility of assembling and formed with a hole 2 therethrough or blocks being L, U, W or likewise shaped in section and provided with one or more vertical grooves 2 or recesses as shown in FIGS. 3 to 7. In either case, they are so shaped as to facilitate heaping one upon another combining altogether in block assembly while forming one or more vertical holes or bores through the entire assembly.

The desulfurizing blocks according to the invention are placed side by side and one upon another or assembled together on a base equipped with corner posts of iron in such a manner that the holes or grooves formed through the individual blocks can communicate with one another to form vertical holes hrough the entire asembly, and then an expanded metal 3 having a lattice of spaces 4 as shown in FIG. 8 or a sheet iron 3 punched with holes 4 as in FIG. 9 or 10, or a sheet iron or the like is fitted as a cover onto the top of the assembly to a unitary construction.

FIG. 11 is a perspective view of an assembly of the desulfurizing blocks 1 which are placed side by side and one upon another over the base members 5 and 6 provided with corner posts of iron and covered with a punched sheet iron 3 on the top to an integral unit. The holes 4 formed through the sheet iron are substantially aligned to the individual holes or grooves through the deforming blocks.

FIG. 12 is a vertical sectional view of a unitary assembly of a certain number of desulfurizing blocks according to the invention as placed in a vessel 7 for containing molten pig iron. In the arrangement shown, which represents a section taken on the line A-A' of FIG. 10, the holes 4 formed through the sheet iron 3 correspond to the through holes or grooves 2 of the individual desulfurizing blocks 1 in vertical communication therewith.

FIG. 13 shows an assembly of desulfurizing blocks 1 of the invention as assembled on a base 5 equipped with corner frames of iron and bound together with fiat steel bands 8 or the like.

The present invention is the composition and configurations of an agent for eliminating sulfur from molten pig iron easily and efliciently without recourse to mechanical power, and the mechanism of the desulfurizing reaction involved.

Soda ash the essential component of the desulfurizing agent according to the invention, is most responsible for the desulfurizing action. It can be preferably used the soda ash having the following purity:

Portland cement, another component of the agent, avoids resulfurization because CaO which constitutes a preponderance of the cement composition undergoes a subsitution reaction with Na s that is produced by the reaction Formula 1 above and thereby forms more stable CaS. It also serves as a binder.

While the desulfurizing agent of the invention has the composition and configuration as described hereinabove, it should be noted, in particular, that the agent is shaped to polygonal cubes or blocks with large areas to contact molten pig iron so that, when floated on the molten metal, the blocks are always immersed partly but deep into the melt, unlike conventional desulfurizing agents of other forms. The size of the molded blocks is increased in proportion to the volume of the melt to be desulfurized. A usually preferable range of the size is between 3 and 500 mm, for each side.

The present invention is illustrated by the following examples, in Which the use of the desulfurizing agent and process according to the present invention are compared with the use of soda ash powder and moldings.

Examples of the composition of the desulfurizing agent according to the present invention are shown in the following table.

Since soda ash is principally responsible for the desulfurizing action .of the agent according to the invention, it is desired to account for as large percent as possible of the composition. However, the percent by weight is limited to 60 to 85 by the necessity of presence of other effective ingredients.

Portland cement not only avoids resulfurization because its major constituent CaO reacts for substitution with sulfide of soda that is produced by the reaction Formula 1 and thereby forms stable Na S, but also serves as a binder. To attain these ends, it is suitably used in the range of 3 to 25% by weight of the total amount of the desul furizing composition. When used in an amount of less than 3%, the cement is unable to act as a binder and fails to maintain the strength of the moldings. With an increase in the amount, its adds accordingly to the strength of the resulting moldings, but it should not be employed in excess of 25% because it brings too much calcium and silicate into the composition for ready melting of the agent and it thus reduces the desulfurizing effect of the agent.

Water glass is used as a quick hardening agent that promotes the setting of portland cement. It is added in an amount of not more than 10% by Weight to a desulfurizing composition for introduction into a large molten pig iron ladle. Any amount exceeding 10% is not desirable since the silicate content is increased to such an extent that it hinders the melting of the desulfurizing agent. Where the desulfurizing agent is to be introduced into a receiver or small ladle for molten pig iron, the use of water glass is not necessary.

Borax and sodium chloride are sometimes required for the adjustment of slag viscosity. In such case they are employed in the range of 0 to 5% by Weight each. Usually they need not be used in amounts of more than 5%. A calcium-containing substance such as calcium oxide, calcium carbonate, calcium hydroxide, calcium fluoride, or calcium chloride is used in an amount of not more than 10% by weight in order to avoid resulfurization as it forms stable calcium sulfide through a substitution reaction with sulfide of soda that is obtained by the reaction Formula 1. Any amount exceeding 10% is objectionable because it hampers melting of the desulfurizing agent.

A carbonaceous substance such as coke, graphite, or charcoal is used to raise the temperature of molten pig iron when it is at a realtively low temperature and also to make up for the loss due to combustion of carbon in the molten pig iron during the course of the desulfurization reaction with soda ash and calcium oxide.

If the melt temperature is too low, the further drop of the temperature due to the endothermic reaction with the desulfurizing agent may render subsequent operation impossible. In the case of molten pig iron with a low carbon content, this may lead to consumption of the carbon content during the desulfurization beyond the allowable limit, thus making it necessary to add carbon and heat the molten pig iron. It is for this reason that such a carbonaceous substance is used in an amount of not more than 5% by weight. Any excess of the amount simply burns on the surface of the molten metal and the effect that is achieved is, in essence, little different from the eifect with 5% only. Rather, it merely reduces the relative proportions of the other efiective ingredients of the desulfurizing agent.

Iron powder is incorporated with the view to increasing the apparent specific gravity of the desulfurizing agent. In the case where a large volume of molten pig iron is to be handled which tends to cause floating up of the desulfurizing agent or where the viscosity of the slag that flows out together with the molten pig iron is high, no effective desulfurization is accomplished unless the apparent specific gravity of the desulfurizing blocks is increased sufliciently to permit the blocks to sink below the surface slag layer and in contact with the molten metal. It therefore should be obvious that the desulfurizing blocks have the greatest apparent specific gravity possible. If the desulfurizing blocks are to sink under the slag layer without difliculty, they should have an apparent specific gravity of at least 1.3. When the composition is molded without inclusion of iron powder, it can have an apparent specific gravity of up to 1.8. But when an even higher value is desired, inclusion of some heavy substance is necessary. In the sense that it does not aifect the properties of the particular molten pig iron, iron powder of the same kind is most preferred for such purpose.

With 10% by weight of iron powder contained, the apparent specific gravity of the desulfurizing agent can be varied over a range of 1.8 to 2.5. Any amount exceeding 10% is not desirable in that the contents of other effective ingredients of the desulfurizing agent must be decreased accordingly, though the apparent specific gravity of the agent as a Whole can be increased. With an apparent specific gravity of up to 2.5, the purpose of sinking the desulfurizing blocks below the slag layer can be fully achieved.

The water content of the desulfurizing blocks is suitably between 7 and 15% by weight. A water content of less than 7% makes the blocks readily collapsible and difficult to handle, while blocks containing more than 15% water are not desirable because of the too violent reaction with molten pig iron that comes into contact.

The shapes of the desulfurizing blocks according to the present invention are such as shown in FIGS. 1 to 7, having one or more through holes or grooves which extend straightly from one side to the other.

Thus, the blocks have polygonal and cubic shapes so that they have large areas in contact with molten pig iron and are partly immersed deep into the melt as they float thereon. Preferably the individual blocks have large sizes when to be used with large volumes of molten pig iron; they should measure not smaller than 30 mm. for each side.

If the moldings are smaller than 30 mm. they are as inadequate and ineffective as powdery or granular desulfurizing agents in the treatment of small volumes of molten pig iron. Procedures for desulfurizing molten pig iron in large-capacity ladles consisting in the use of a desulfurizing agent according to the present invention, either in the form of a unitary assembly of a predetermined quantity of the blocks as shown in FIG. 11 or FIG. 15 or in the form of a single block as shown in FIG. 14 which is large enough to accomplish the desulfurization of molten pig iron in the particular vessel, and which is preset in the ladle as shown in FIG. 12, and subsequent pouring of molten pig iron into the ladle for desult-urization. The molded blocks of the desulfurizing agent are placed side by side and one upon another or assembled together in such a way that their respective through holes or grooves run up and down in communication with ane another, thereby forming a multiplicity of substantially vertical holes which extend from the top end to the bottom of the assembly. As molten metal is poured into the ladle in the manner above described, the melt flows down through the holes of the desulfurizing blocks and reaches the bottom of the vessel, with the consequence that the desulfurizing blocks as a whole float up 6 and the molten pig iron continuously poured in therethrough takes the same course and is thereby freed from sulfur.

The dimensions of the molded blocks of the desulfurizing agent are so adjusted that the time during which the desulfurizing agent collapses in contact with molten pig iron substantially corresponds to the pouring time. Since all the molten pig iron poured into the ladle flows down through the surface of the desulfurizing blocks, a perfect contact is ensured between the molten pig iron and the desulfurizing agent without the application of any external force. With no such disadvantage of non-homogeneity due to agitation with external force of a large amount of molten metal in a large ladle, the pouring time is directly taken advantage of in accomplishing the desulfurization within a short period of time to a great practical advantage.

The present invention is further characterized by the use of portland cement which can produce stable CaS as a component of a desulfurizing agent for molten pig iron and also as a binder. By the same token, it provides molded shapes of desulfurizing agent having certain formulations and configurations and permits des-ulfurization of molten pig iron extremely effectively with the use of a desulfurizing agent of certain shapes in certain ways. Thus, the desulfurizing agent and process according to the present invention are far more advanced and industrially advantageous over the conventional ones.

What I claim is:

1. A homogeneous molded desulfurizing agent for molten pig iron having a specific gravity of between 1.3 and 2.5 and being a homogeneous composition consisting only of: to 85% by weight of soda ash, 3 to 25% by weight of portland cement, 0 to 10% by weight of water glass, 0 to 5% by weight of borax, 0 to 5% by weight of sodium chloride, 0 to 10% by weight of a calcium-containing substance, 0 to 5% by weight of a carbonaceous substance, 0 to 10% by weight of iron powder, and 7 to 15% by weight of water.

References Cited UNITED STATES PATENTS 2,117,348 5/1938 Muskat -57 X 2,462,871 3/1949 Kinzel 75-58 X 2,550,735 5/1951 Tour 7558 X 3,051,564 8/1962 Drenning 7558 X 3,258,328 6/1966 Goss 7557 L. DEWAYNE RUTLEDGE, Primary Examiner J. E. LEGRU, Assistant Examiner US. Cl. X.R. 7553 

